Imaging surgical target tissue by nonlinear scanning

ABSTRACT

Systems and techniques for laser surgery based on imaging a target tissue by nonlinear scanning are presented. In one implementation, a method for guiding an eye surgery can include the steps of: positioning an eye in relation to an imaging system; creating first scan data by determining a depth of an eye target region at a first set of points along a first arc; creating second scan data by determining a depth of the eye target region at a second set of points along a second arc; determining target region parameters based on the first and second scan data; and adjusting one or more surgical position parameters according to the determined target region parameters.

TECHNICAL FIELD

This patent document relates to systems and techniques for surgicalapplications, including ophthalmic surgery.

BACKGROUND

A variety of advanced surgical laser systems have been developed overthe years for ophthalmic surgery, targeting portions of the cornea, thelens, the retina and other structures of the eye. Such a surgical systemcan employ an imaging mechanism to obtain images of a targeted surgicalregion to assist the operator of the surgical system, e.g. the surgeon,to place laser pulses in the targeted surgical region of the eye withhigh precision.

SUMMARY

This document discloses examples and implementations of systems andtechniques for laser surgery based on imaging a target tissue bynonlinear scanning during the imaging.

For example, a method for guiding an eye surgery can include the stepsof: positioning an eye in relation to an imaging system; creating firstscan data by determining a depth of an eye target region at a first setof points along a first arc; creating second scan data by determining adepth of the eye target region at a second set of points along a secondarc; determining target region parameters based on the first and secondscan data; and adjusting one or more surgical position parametersaccording to the determined target region parameters.

In some implementations, the determining the depth includes imaging theeye target region with at least one of an optical coherence tomography(OCT) method, an ultrasound-based method, a microscopic method and aninterference based method.

In some implementations, the eye target region is one of a cornealtarget region, an anterior lens surface, a posterior lens surface, alens target region, an ophthalmic layer, and a surface defined by apupil.

In some implementations, at least one of the first arc and the secondarc forms at least part of a closed loop.

In some implementations, the first arc is a portion of a firstintersection line where a first scanning surface intersects the eyetarget region; and the second arc is a portion of a second intersectionline where a second scanning surface intersects the eye target region.

In some implementations, the first arc is a portion of a firstintersection line where a first cylinder intersects the eye targetregion; and the second arc is a portion of a second intersection linewhere a second cylinder intersects the eye target region.

In some implementations, the first cylinder and the second cylinder areconcentric, sharing a Z axis.

In some implementations, a Z axis of the second cylinder is offset froma Z axis of the first cylinder.

In some implementations, the determining target region parameters stepincludes extracting scan characteristics from the first and second scandata.

In some implementations, the extracting scan characteristics stepincludes extracting a first amplitude and a first phase of the firstscan data; and extracting a second amplitude and a second phase of thesecond scan data.

In some implementations, the determining of target region parametersstep includes determining a position parameter of a center of the targetregion based on the first amplitude, first phase, second amplitude andsecond phase.

In some implementations, the determining of the target region parametersstep includes determining an object shape parameter of the target regionbased on the first amplitude, first phase, second amplitude and secondphase.

In some implementations, the determining of the target region parametersstep includes determining an object orientation parameter of the targetregion based on the first amplitude, first phase, second amplitude andsecond phase.

In some implementations, the determining of the target region parametersstep includes determining a position parameter update, related to aposition of the target region and a reference point.

In some implementations, the adjusting the surgical position parameterincludes adjusting a position parameter of a surgical pattern center toalign the surgical pattern center with a center of the target region.

In some implementations, the method contains no more scans after thefirst scan and the second scan.

In some implementations, the time from the starting of the firstscanning step to the finishing of the determining the surgical positionparameters step is no more than one of 100 milliseconds, 1,000milliseconds and 10,000 milliseconds.

In some implementations, at least one of the first and second arc iselliptical.

In some implementations, at least one of the first arc and the secondarc is an open arc; and at least one of the first scan data and thesecond scan data have a maximum and a minimum.

In some implementations, the eye target region is a region of a lens ofthe eye, the target region parameters include a shape parameter of thelens, a tilt parameter of the lens, and a position parameter of thelens.

In some implementations, the determining target region parameter stepincludes fitting a function with at least one fitting parameter to thefirst scan data; and determining the target region parameter using thefitting parameter.

In some implementations, a method for imaging an object includes thesteps of positioning the object relative to an imaging system, wherein ashape of the object is describable in terms of one or more shapeparameter; creating scan data by determining a coordinate of the objectat a set of points along an arc; and determining an object shapeparameter and an object position parameter based on the scan data.

In some implementations, the object is a portion of a spherical surfacelayer; and the determined object shape parameter is a radius of thespherical surface layer.

In some implementations, the object is an anterior lens surface layer ofan eye; the object shape parameter is a radius of the anterior lenssurface layer; and the object position parameter is a coordinate of acenter of the anterior lens surface.

In some implementations, the determining the object position parameterstep includes imaging the object with at least one of an opticalcoherence tomography (OCT) method, an ultrasound-based method, amicroscopic method and an interference based method.

In some implementations, the determining the object shape parameter andthe object position parameter step includes creating auxiliary scan databy determining a coordinate of the object at an auxiliary set of pointsalong an auxiliary arc.

In some implementations, the determining the object shape parameter andthe object position parameter step includes determining the object shapeparameter and the object position parameter from the scan data and theauxiliary scan data.

In some implementations, the position parameter of the object is a Zcoordinate of an object layer; and the arc is a portion of anintersection line where a scanning cylinder intersects the object layer.

In some implementations, the determining the object shape parameter stepincludes determining the Z coordinate of the object layer at theauxiliary set of points along an intersection line where an auxiliarycylinder intersects the object layer.

In some implementations, the scanning cylinder and the auxiliarycylinder are essentially concentric, sharing a Z axis.

In some implementations, the determining the object shape parameter andobject position parameter step includes extracting an amplitude and aphase of the scan data; and determining a center of the object layerbased on the extracted amplitude and phase.

In some implementations, the object position parameter is one of aparameter of a center of the object layer and a perimeter of the objectlayer.

In some implementations, the method contains no more scans after thescan and an auxiliary scan.

In some implementations, the determining of the object positionparameter and the object shape parameter are performed in an integratedmanner.

In some implementations the object is one of a closed object and an openobject.

In some implementations, a method for guiding eye surgery includes thesteps of (a) positioning an eye relative to a surgical laser system, thesurgical laser system having a surgical position parameter and the eyehaving a lens; (b) determining position data of a lens target regionalong a scanning arc; (c) determining a lens position parameter based onthe position data; (d) adjusting the surgical position parameteraccording to the determined lens position parameter; and (e) repeatingsteps (b)-(d) during the eye surgery to readjust the surgical positionparameter.

In some implementations, the lens target is one of an anterior lenssurface, an anterior surface defined by a pupil, a lens target region,and a posterior lens surface.

In some implementations, the determining of the lens position parametersstep includes extracting an amplitude and a phase of the position data.

In some implementations, the determining of the lens position parametersstep includes determining a position parameter of a center of the lenstarget based on the amplitude and phase of the position data.

In some implementations, the adjusting a surgical position parameterincludes adjusting a position parameter of a surgical pattern center toalign a surgical pattern in three dimensions with respect to acharacteristic feature of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-C illustrate a targeting offset in ophthalmic laser systems.

FIG. 2 illustrates an existing targeting method.

FIG. 3 illustrates an embodiment of a method to guide an eye surgery.

FIGS. 4A-E illustrate the steps of the method of FIG. 3.

FIGS. 5A-B illustrate an adjusting of a surgical position parameter.

FIGS. 6A-B illustrate embodiments of imaging methods.

FIG. 7 shows an example of an imaging-guided laser surgical system inwhich an imaging module is provided to provide imaging of a target tothe laser control.

FIGS. 8-16 show examples of imaging-guided laser surgical systems withvarying degrees of integration of a laser surgical system and an imagingsystem.

FIG. 17 shows an example of a method for performing laser surgery bysuing an imaging-guided laser surgical system.

DETAILED DESCRIPTION

Many eye surgical devices include a docking stage, which makes contactwith the eye and keeps it effectively immobile relative to the objectiveof the surgical system. To guide the surgical procedure, certain systemsgenerate a target pattern, which indicates the center of the objectivewhere the surgical laser is focused. These systems display the targetpattern over the image of the eye to guide the surgeon to apply thelaser beam precisely to the intended target region of the eye.

FIGS. 1A-B illustrate the operation of an example of such image guidedsurgical systems. When the docking stage or objective is docked to theeye by the surgeon, the target pattern 40 may not be centered perfectlyrelative to the eye so that the center of the target pattern 40 may havebe offset in position from the center of the eye.

FIG. 1A illustrates such a case when the target pattern 40 is not wellcentered with any one of prominent structures of the eye, such as thepupil 10, the iris 20 or the limbus 30. This misalignment poses adifficulty for the eye surgeon to place the laser pulses with highprecision on the intended target within the eye.

An advanced image guided surgical laser system may be designed toextract information about the degree of the misalignment and to adjustthe location of the target pattern 40 to be centered relative to aselected eye structure, such as the pupil 10. FIG. 1B illustrates anadjusted alignment in such a system that essentially eliminates theoffset shown in FIG. 1A. In such an advanced system the target pattern40 can be shifted to the center, enabling a subsequent high precisionapplication of the surgical laser beam.

The higher the precision of the targeting system, the more efficient theophthalmic surgery. Therefore, while a manual adjustment of the targetpattern 40 is possible, computer-based automated alignment adjustmentscan be used to improve the precision of image guided systems and toovercome the problem of the misalignment.

FIG. 2 illustrates the operation of one example of a computer-basedautomated alignment adjustment. In this example, scans are performedalong straight lines, and the linear scans are performed repeatedly anditeratively. While each linear scan provides only incomplete informationregarding the misalignment, the repeated iterations improve the guidancehow to move the center of the target pattern 40 closer and closer to thecenter of the target region.

Examples and implementations of systems, apparatus and techniques areprovided in this document for laser surgery based on imaging a targettissue by nonlinear scanning during the imaging. The imaging informationobtained from the nonlinear scanning is used to guide the laser beam forperforming the laser surgery on the target tissue.

FIG. 3 illustrates a method for guiding an eye surgery 100, whichincludes the steps of: positioning an eye in relation to an imagingsystem 110; creating first scan data by determining a depth of an eyetarget region at a first set of points along a first arc 120; creatingsecond scan data by determining the depth of the eye target region at asecond set of points along a second arc 130; determining target regionparameters based on the first and second scan data 140; and adjustingone or more surgical position parameters according to the determinedtarget region parameters 150.

The positioning step 110 can include a wide variety of known methods,including applying a suitable type of a patient interface. Onepossibility is to lower a gantry supporting a patient interface and anobjective of the surgical system onto the eye.

The patient interface can have a flexible skirt, partially made of anelastic material, surrounding an optical targeting system of a surgicalsystem, such as the objective. The patient interface can include suctioncups. Once the patient interface has been positioned on the eye, vacuumcan be applied under the flexible skirt of the suction cup to establisha mechanical connection and stabilizing force between the eye and thepatient interface. The suction cup can apply the vacuum to a largeportion of the eye or to a ring-like region of the eye.

In other implementations, the patient interface can include a corrugatedsurface, which establishes a grip on the eye by making small and gentleindentations into the surface of the eye. These embodiments may positionthe eye without applying a vacuum. Yet other embodiments can apply somedegree of pressure to establish a mechanical connection. Embodiments canestablish the mechanical connection via a portion of the eye: within asurgical region, around a perimeter of the surgical region, or an outerregion of the eye. Some embodiments may position the eye by other means,including non-mechanical connections.

The degree of the mechanical connection can be of widely varying type:in some implementations the eye can be firmly connected to the patientinterface, preventing motion of the eye relative to the patientinterface. In other embodiments, the connection can be of intermediatestrength, allowing some degree of relative motion of the eye. In somecases certain type of relative motion can be allowed, such as motionalong an optical axis, or transverse to the optical axis. In someembodiments, the positioning may not involve direct mechanical contactto a patient interface.

The positioning can also include varying degrees of applanation of theeye contact surface. In some cases the contact surface of the eye isessentially flattened, in others the contact surface can be onlypartially flattened, and in yet others the natural curvature of the eyemay remain essentially unchanged.

Referring back to FIGS. 1A-C, the eye surgical procedure can utilize asurgical target pattern 40. The reference framework defined by thistarget pattern 40 can be used by the surgeon to direct a surgical laserbeam to a precisely defined location within the surgical region of theeye. The target pattern 40 can be displayed e.g. on a video-microscopeor an other type of display device. The target pattern 40 can be shownoverlaid with the image of the eye on the video-microscope. In otherembodiments, the target pattern 40 can be only a construct of a softwareprogram, not necessarily displayed anywhere. In some of theseembodiments, the software may only track the center of the targetpattern 40 and can guide the surgeon based on the location of thecenter. In semi-, or fully automatic embodiments the software of thesystem can carry out the guiding steps described below, without everdisplaying an explicit target pattern 40.

At the start of the surgical proceedings, the target pattern 40 may becentered at the physical or geometrical center of the patient interfaceor the objective. Since the patient interface can be rarely positionedand docked to be perfectly aligned with the center of the eye in step110, the target pattern 40 typically needs shifting or adjustment afterthe positioning/docking so that it is aligned well with a center of theeye or with an identifiable structure of the eye. Here the center of theeye may refer to a center of a selected structure of the eye, includingthe pupil 10, the iris 20, the limbus 30, or the lens 50. Theidentifiable structure can be an identifiable limbic structure, bloodvessel, the fovea, the optic disc or another structure.

The eye structures, such as the lens 50 and the pupil 10 often do notshare a common center. This can occur e.g. because of some inherentasymmetry of the eye, or because the pressure from the patient interfacemay have moved or tilted the lens 50 relative to the pupil 10.

FIGS. 1A-C illustrate that in this typical situation the operator of theimaging system may perform a first shift of the target pattern 40 fromits initial, off-center position in FIG. 1A to be aligned with aprominent eye structure, such as the pupil 10, indicated by once shiftedtarget pattern 40′ in FIG. 1B. This can be done manually or in apartially or fully automated manner. In ophthalmic procedures whichtarget the lens 50, if the pupil 10 and the lens 50 share a center, thencentering the target pattern 40 to the pupil 10 completes the adjustingmethod and the surgeon can use this once shifted target pattern 40′ toguide the lens surgery.

FIG. 1C illustrates the case when the lens 50 is not aligned with thepupil 10. In this case, after the first shift of the target pattern 40′to align it with the pupil 10, in a subsequent second step the operatorcan practice the guiding method 100 to identify how much the onceshifted center of the target pattern 40′ and the pupil 10 is still offthe center of the lens 50, and perform a second shift of the targetpattern 40′ to be aligned with the center of the lens 50, as shown bytwice shifted target pattern 40″ in FIG. 1C.

In some implementations, the first and the second shift of the targetpattern 40 can be performed in a single integrated step by practicingthe guiding method 100 to shift the target pattern 40 from its initial“as-docked” position to the center of the lens 50.

Once the target pattern 40 is aligned with the targeted surgical region,such as centered to the center of the lens 50, a surgical laser can beapplied to perform a surgery on the lens 50 using the reference frame ofthe target pattern 40.

A location of the target pattern 40 can be stored e.g. in a computercontroller of the surgical system. In some implementations, a videointerface may overlay an image of the target pattern 40 and an actualimage of the eye on a video microscope. Among others, such a compositepicture illustrates the degree of the de-center of the target pattern 40from a center of a selected eye structure, such as the pupil 10. Suchoverlaid composite images can be helpful to perform the first shift,aligning the target pattern 40 with e.g. the pupil 10.

It is noted that the first and second shifts (or the integrated singleshift) move the target pattern 40 away from the center of the patientinterface or the objective. With a sufficiently good design of thesurgical optics, the subsequently applied surgical lasers may preservetheir low astigmatism and other aberrations even when applied to thisshifted off-center target region.

Examples of surgical procedures which benefit from a precisely targetedsurgical laser include capsulotomy, i.e. cutting a circle into thecapsule of the lens 50 for the purpose of inserting an Intra Ocular Lens(IOL) in place of a removed existing lens. A high precision centering ofthe capsulotomy cut allows a high precision centering of the insertedIntra Ocular Lens (IOL), optimizing the outcome of the cataract surgery.

Another example is the fragmentation or liquefication of the lensitself, which is performed in preparation for the removal of the lensfrom the lens capsule. In general, it is beneficial to remove as large afraction of the lens as possible, while making sure not to puncture theposterior surface of the lens capsule. A low precision targeting systemmay force the surgeon to leave a thicker layer of the lens in thecapsule just to make sure not to puncture the posterior capsule surface.In contrast, a system which positions the target pattern 40 with highprecision can allow cutting very close to the posterior capsule surface,improving the efficiency of the cataract surgery.

It is noted that the target pattern 40 can be one of a wide variety ofpatterns, including one or multiple concentric circles, a cross-hairpattern, another indication of a center of the pattern, or one or morerectangular elements, and a combination of the above. The pattern mayhave variable elements, e.g. one of the lines can change color, oradditional lines may appear to indicate any of the steps of the method,such as the successful completion of the positioning of the eye in step110, or the successful readjusting of the surgical positions parametersin step 150.

It is further noted that the application of the surgical laser canfollow a surgical pattern, which can be different from the targetpattern in general. The surgical pattern can be a very wide variety ofpatterns, including circles, cylinders, sequential layers, spirals, 4,6, or 8 fold radial partitioning, and other chopping patterns. In thecontext of the present guiding method 100, the position of this surgicalpattern can be adjusted according to the shifted target pattern in step150. In the simplest case, the center of the surgical pattern can bealigned with the center of the target pattern 40. But a wide variety ofalternative adjustments are also possible, such as centering thesurgical pattern with a shift relative to the center of the targetpattern 40, or placing a starting location of the surgical pattern to aspecific point of the target pattern, etc.

In some implementations, the determining the depth in steps 120 and 130can include: imaging the eye target region with an optical coherencetomography (OCT) method, an ultrasound-based method, a microscopicmethod and an interference based method, or a combination of thesemethods. The optical coherence tomography method can be implemented as atime domain or a frequency domain tomography.

In some of the subsequent sections, the guiding method 100 will bedescribed in the context of performing the above described second shiftor integrated shift of the target pattern 40. Both implementationsinvolve determining the misalignment of the target pattern 40 and thecenter of the eye target region, such as the lens 50.

The eye target region can be a corneal target region, an anterior lenssurface, a posterior lens surface, a lens target region, an ophthalmiclayer, or a surface defined by a pupil. The term “surface” is used in abroad sense, referring not only to an outermost geometrical surface, butto surface layers with some thickness. Surface layers can be definede.g. by their biological, optical or mechanical properties and can havea layer thickness from a micron or less to a millimeter or more. Also,the term “layer” can refer to a layer inside a structure of the eye.

The surgical regions may be targeted in various ophthalmic surgicalprocedures, including corneal procedures, cataract procedures,capsulotomy, lens lysis or fragmentation. The target region can be thetarget region of the ophthalmic procedure itself, such as a lenssurface, or an auxiliary target region, e.g. a region where an accesscut is created on the cornea to facilitate a lens procedure.

FIG. 4A illustrates an implementation of method 100. In step 110 apatient interface 210 can be brought into mechanical contact with acornea 220 of an eye to position the eye for an ophthalmic surgery. Forexample, the patient interface 210 can immobilize the eye and its cornea220 by applying a partial vacuum.

The step 120 can include determining a depth 241-D1, . . . 241-Dn of aneye target region in the lens 50 at a first set of points 241-P1, . . .241-Pn along a first arc 241 and storing the depth values 241-D as thefirst scan data.

The analogous step 130 can involve determining a depth 242-D1, . . .242-Dn at a second set of points 242-P1, . . . 242-Pn along a second arc242 and storing the depth values 242-D as the second scan data.

In some implementations, at least one of the first and the second arcscan be part of or the entirety of a closed loop. The loop can be acircle, an ellipse, a partially irregular loop, or a suitably shapedloop. In other implementations the arc can be an open arc, which is aportion of a circle, ellipse, or other suitable curve.

In some implementations, the arcs, or open or closed loops, 241 and 242can be centered at the center of the target pattern 40. Therefore, afterthe offset of the center of the loops 241 and 242 from the center of thetarget region is determined, the center of the target pattern 40 can bealigned with the center of the target region by shifting the center ofthe target pattern 40 by the offset of the loops 241 and 242. In severalof the below embodiments the first and second arcs 241, 242 share acenter with the target pattern 40.

Arcs can be a wide variety of lines, distinguished from the straightlines of FIG. 2 by their non-negligible curvature in the XY plane, i.e.the plane transverse to the optical axis (commonly referred to as the Zaxis). It is noted that even the straight lines of FIG. 2 may have somecurvature in planes containing e.g. the Z and X, or Z and Y axes.However, since they appear as straight lines on a view of the XY plane,i.e. when projected onto the XY plane, they will not be termed an arc.

FIG. 4B illustrates that in some embodiments, the first arc 241 can be aportion of a first intersection line where a first scanning surface 245intersects an eye target region, e.g. the anterior surface region of thelens 50. Analogously, the second arc 242 can be a portion of a secondintersection line where a second scanning surface intersects the eyetarget region.

Here the scanning surface 245 can refer to the surface swept by ascanning beam as a characteristic point of the scanning beam, such asits focus point, is moved along a line in the target region.

In the example of FIG. 4B, a focal point of a scanning laser beam can bemoved along a circle in an XY plane. The scanning laser can beessentially parallel to the optical Z axis of the optical system,defining a cylinder as the scanning surface 245. Visibly, in thisexample the first arc 241 is the loop where the cylindrical scanningsurface 245 intersects the ellipsoidal lens 50. Depending on theposition of the center of the cylindrical scanning surface 245, thefirst arc 241 can be a circle or an ellipse. The plane of the circle orellipse 241 can be transverse to the Z axis, i.e. it can be the XYplane, if the center of the circle 241 coincides with that of the lens50. In other words, if the circle 241 shares the symmetry axis with thelens 50. If the circle 241 does not share its symmetry axis with thelens 50, or equivalently the center of the circle 241 does not coincidewith the center of the lens 50, then the plane of the circle 241 can betilted, as in FIG. 4B.

FIG. 4C illustrates embodiments where the first and second arcs 241 and242 are closed loops, e.g. circles. In the left panel the first andsecond scanning cylinders and their corresponding loops 241 and 242 areconcentric, sharing an optical, or Z axis. In the right panel, the loops241 and 242 are not concentric, having their axes offset relative toeach other. They may or may not intersect each other. Differentembodiments may extract target-center-adjustment information better fromconcentric scanning circles, while others from offset scanning circles.

FIG. 4D illustrates how the target region parameters can be determinedin step 140 based on the first and second scan data. In the left panel acircular scanning arc 241 is shown with its center 241-C offset from acenter 50-C of the surgical target region, which is the lens 50 in thiscase. As described in the introduction, this or analogous situations canoccur when the patient interface 210 is docked with its center off thecenter of the surgical target region.

In such situations, the surgical optical system may be operated in a waythat compensates for this offset by, e.g., aligning the center of thetarget pattern 40 with the center of the lens 50-C. As discussed above,in various embodiments the center of the target pattern 40 coincideswith the shared center of the first and second scanning arcs 241-C and242-C. Thus, this task of aligning the centers translates to determiningthe offset of the center of, e.g., the first arc 241-C from the targetcenter 50-C. Once this offset is determined, the center of the targetpattern 40 can be shifted by this offset to align it properly with thelens-center 50-C. Subsequently, a surgical pattern can be defined usingthe properly centered target pattern 40 and the surgical laser beam canbe applied according to the surgical pattern.

As described below, this adjustment may be based not only on the centerof the surgical target region, but on various characteristic features ofthe surgical target region, such as a characteristic feature, a spotcoloration, an irregular feature, a blood vessel, etc.

One method to facilitate such an adjusting is to extract first andsecond scan characteristics from the first and second scan data.Examples of these scan characteristics include a first amplitude and afirst phase of the first scan data; and a second amplitude and a secondphase of the second scan data.

As shown in the right panel of FIG. 4D, when the first loop 241 is anoffset circle or ellipse on the target surface, the first scan, ordepth, data 241-D1, . . . 241-Dn of the first arc-points 241-P1, . . .241-Pn form a section of a sinusoidal curve. In general, this curve canbe a function which can be represented by a Fourier sum of harmonics. Ifthe scanning circle 241 is perfectly centered at the center of thetarget region, i.e. 241-C coincides with 50-C, then the first scan, ordepth data will be a constant function.

If the first arc is a full circle, then the sinusoidal curve can have afull period of a sinusoidal. Typically, the scans do not start at themaxima or minima of the sinusoidal, thus the first scan, or depth, data,when plotted as a function of a distance along the scanning arc 241,take the shape of a sinusoidal starting with a phase shift.

FIG. 4E illustrates that in such a case the first scan characteristicscan be e.g. a phase F1 and an amplitude A1 of the sinusoidal of thefirst scan, or depth, data 241-D1, . . . , 241-Dn. These scancharacteristics can be determined by fitting a sinusoidal function tothe first scan, or depth, data, and treating the adjustable phase andamplitude of the sinusoidal as fitting parameters. Similarly, a secondscan characteristics of a second amplitude A2 and second phase F2 can beextracted from fitting a sinusoidal to the second scan, or depth, data242-D1, . . . 241-Dn.

In general, if the center of the scanning loop, and thus typically thecenter of the target pattern 40, coincides with the center of the lens50, the scan data 241-D1, . . . 241-Dn are a constant, translating to azero amplitude for the sinusoidal. The more offset the center of thescanning loop 241-C from the center of the lens 50, the larger theamplitude A1. Therefore, the amplitude A1 can characterize how faroffset the center of the scanning loop 241-C and thus the target pattern40 is relative to the center 50-C of the target region. The phase F1 maycharacterize which direction the shared center of the scanning circle241-C and the target pattern 40 is offset from the center 50-C of thetarget region.

Such phase and amplitude scan characteristics can be extracted if thescanning arc 241 is not a circle, but an ellipse, or even an open arc.In the case when the scan data can be fitted not with a singlesinusoidal, but with the sum of several, e.g. m, Fourier harmonics, theamplitudes A1, . . . Am and phases F1, . . . Fm of each of these Fourierharmonics can be extracted by standard fitting procedures. One or moreof these amplitudes A1, . . . Am and phases F1, . . . Fm, or a subset ofthese amplitudes and phases can be used as scan characteristics.

Also, in some implementations, the scan characteristics can be a largevariety of other characteristics, which are helpful for the eventualadjusting of center of the target pattern 40. Such scan characteristicscan be the depth values at specific scan points themselves, gradients ofthe depth data points, triangulation related data, various moments ofthe fitted sinusoidal, or a characteristic of the higher harmonics. Insome implementations the first and second scan data can exhibit amaximum and a minimum, and the scan characteristics can be related tothese minima and maxima. The scan characteristics can be a suitableparameter or data, which can be used for the shifting of the targetpattern 40.

FIG. 5A illustrates that the determining the target region parametersstep 140 may include determining a position parameter of a center of thetarget region 50-C based on the first amplitude A1, the first phase F1,the second amplitude A2 and the second phase F2. E.g. a computercontroller can establish a coordinate system centered at the sharedcenter 241-C of the scanning loop 241 and the target pattern 40. Usingthe first and second amplitudes A1, A2 and phases F1, F2, the C_(x) andC_(y) coordinates of the center of the target region 50-C can bedetermined relative to this coordinate system. These C_(x) and C_(y)coordinates are the sought after offset, or target region parameters, bywhich the center of the target pattern 40-C is to be shifted to alignwith the center of the target region, such as the lens 50-C.

In detail, this determining of the target region parameters step can bestated in general as:TRj=TRj(Ai,Fi)  (1)

where TRj denote the target region parameters TR1 and TR2, Ai denote theamplitudes and Fi denote the phases, which are specific examples of thescan characteristics. In the specific case above, when the target regionparameters TRi are the Cartesian coordinates C_(x) and C_(y) of thetarget region center within the reference frame of the target pattern40, the above Eq. (1) reads:C _(x) =C _(x)(A1,A2,F1,F2)C _(y) =C _(y)(A1,A2,F1,F2)  (2)

In some implementations, only one scanning circle or loop may besufficient to determine center coordinates C_(x) and C_(y):C _(x) =C _(x)(A1,F1)C _(y) =C _(y)(A1,F1)  (3)

In some other embodiments, the target region parameters TR1 and TR2 arethe direction and the magnitude of the offset of the target center 50-Crelative to the scan loop center 241-C, expressed e.g. in radialcoordinates, which can also be determined from the phase F1, F2 and theamplitude A1, A2 scan characteristics.

In some implementations, the determining of the target region parametersstep 140 can include determining a radius of curvature R parameter ofthe target region based on the first amplitude, first phase, secondamplitude and second phase. An example can be the determination of aradius of curvature R of a cornea 220 or a lens 50. This radius ofcurvature R can be used in the determination of the offset of the targetcenter 50-C from the shared center of the scan loop 241-C and targetpattern 40-C:C _(x) =C _(x)(A1,F1,R(A1,F1))C _(y) =C _(y)(A1,F1,R(A1,F1))  (4)

The sinusoidal behavior of the first scan, or depth data 241-D1, . . .241-Dn may have more than one origin. The above discussed offset of thetarget pattern center 40-C and the target region center 50-C is oneprimary origin. However, other factors can also contribute. Thesefactors include a possible tilt of the optical axis of the eye, and adeviation from a purely spherical shape, such as the target regionhaving an ellipsoidal shape.

These cases can be captured by the general terminology of shapeparameters SPi, orientation parameters OPi and position parameters PPi.The radius of a spherical target R is a simple example of a shapeparameter SP. Ellipsoidal targets can be characterized by three shapeparameters SP1, SP2, and SP3, the length of their three axes a, b, andc. Obviously, the more complex shape the target has, the more shapeparameters are required for its satisfactory characterization.

Completely spherical targets do not have orientation parameters OPisince all directions are equivalent because of their inherent sphericalsymmetry. But the orientation of all targets not possessing suchcomplete spherical symmetry can be captured through orientationparameters OPi. Examples include spherical targets, having adistinguishing region, such as the pupil 10 on an (approximately)spherical eye. Other examples include ellipsoidal targets, where e.g.the components of the vectors, characterizing the orientation of themain axes, are examples of orientation parameters.

Of special interest is the lens 50, which to a good approximation has anellipsoidal shape with two main axes, a and c, as the lens retained itsrotational symmetry around one symmetry axis and thus the third axis bis equal to a. Thus, a and c are examples of the shape parameters SP1and SP2 of the lens 50. The two components of the unit vector,describing the direction of the axis of rotational symmetry, also calledthe tilt vector, are examples of a set of orientation parameters OPi ofthe lens 50.

Finally, the coordinates Ci of the center of the lens 50-C are examplesof the position parameters PPi. The position parameters PPi, theorientation parameters OPi and the shape parameters SPi together are ageneral list of target region parameters TRi.

In a general formulation, all these target region parameters TRi areextracted from the scan characteristics, such as the amplitudes Ai andphases Fi. In a formulation alternative to Eq. (4), these relations canbe captured as:PPj=PPj(Ai,Fi)SPj=SPj(Ai,Fi)OPj=OPj(Ai,Fi)  (5)

While the formulation of Eq. (4) indicated that the shape parameters SPiare determined as an intermediate step of the method, the formulation ofEq. (5) emphasizes that even the shape parameters SPj are determinedfrom the scan characteristics. It is noted that indexing the targetregion parameters TRj differently from the scan characteristics Ai andFi indicates that in general the number of TRj parameters can differfrom the number of scan characteristics Ai and Fi. Typical embodimentsextract a large enough number of scan characteristics Ai and Fi to besufficient to determine all the necessary target region parameters TRj.

In some embodiments, a high fidelity determination of the target regionparameters TRj can include supplementing the scan characteristics Ai andFi with some of the scan data, such as the direct depth data 241-D1, . .. 241Dn as well.

Some implementations of the method 100 use two scanning loops 241 and242. Such a method will be demonstrated on the example of the lens 50.Approximating the lens anterior surface with a spherical one, havingonly one shape parameter SH1=R and formulating the method for the twoposition parameters in the XY plane PP1=Cx and PP2=Cy, the above twoapproaches are represented by the equations:C _(x) =C _(x)(A1,A2,F1,F2,R(Ai,Fi))C _(y) =C _(y)(A1,A2,F1,F2,R(Ai,Fi))  (4′)

-   and    C _(x) =C _(x)(A1,A2,F1,F2)    C _(y) =C _(y)(A1,A2,F1,F2)    R=R(A1,A2,F1,F2)  (5′)

These equations also demonstrate that extracting and using more scancharacteristics than minimally necessary for determining the targetregion parameters TRj, in the present example 4 instead of the minimallynecessary 3, can be an avenue to increase the fidelity of the eventualposition parameters PPj.

FIG. 5B illustrates that the determining of the target region parametersTRj step 140 may include determining a position parameter update,related to a position of the target region and a reference point. In theillustrated example, the reference point is the shared center of thescan loop 241 and target pattern 40, the position related to the targetregion is the center of the target region 50-C, and the positionparameter update is the shift, or offset vector (C_(x), C_(y)) by whichthe center of the target pattern 40 has to be shifted to overlap withthe center of the target region 50-C.

As mentioned above, this shift vector can be given in a wide variety offorms including radial coordinates, indicating an angle of the shift andlength of shift.

Step 140 may include shifting the center of the target pattern 40-C withthe just-determined shift vector (C_(x), C_(y)), so that the center ofthe target pattern 40-C overlaps the center of the target region 50-C.

The step 150 of adjusting the surgical position parameters may includeadjusting a position parameter of a surgical pattern center to align thesurgical pattern center with a center of the target region.

In some embodiments, the surgical pattern can be centered to the centerof the target pattern 40. In these embodiments, step 150 can be carriedout by shifting the shared center of the surgical pattern and the targetpattern from its initial position by the shift vector, or positionparameter update, determined in step 140.

In some other embodiments, first the target pattern can be shifted,followed by the shifting the surgical pattern.

As discussed above, this shift can be a single, integrated shift, or itcan be a two step shift, where the first step may be performed either bypracticing the guiding method 100 or by a manual or partially automatedshift to center the target pattern 40 and the surgical pattern to aneasily identifiable eye structure, such as the pupil 10. This shift canbe followed by the second shift, moving the center of the target andsurgical patterns to the center of the true target region, e.g. the lens50.

In contrast to existing methods, implementations of the guiding method100 can provide such a high accuracy determination of the positionupdate, or shift vector, that typically the guiding method 100 can beperformed only once, and the resulting position update, or shift vectoraligns the surgical pattern with the surgical target region with a highaccuracy. Therefore, in some implementations of the guiding method 100,the steps of the method can be performed only once to yield asatisfactory result.

This is to be contrasted with the limited accuracy of the existingmethods where the steps of the method have to be performed iterativelyand repeatedly, bringing the center of the target pattern closer andcloser to the target region.

This high precision of the present guiding method 100 is particularlyadvantageous in all applications where time is at a premium, such as ineye surgical applications. The fact that the method 100 can be performedonly once to yield high accuracy results means that in someimplementations the time from the starting of the first scanning step tothe finishing of the determination of the surgical position parametersstep can be no more than 100 milliseconds, 1,000 milliseconds and 10,000milliseconds. Each of these characteristic times can have criticaladvantages in time-sensitive applications.

FIG. 6A illustrates that, while the guiding method 100 has beendescribed in terms of an eye surgical application, the describedconcepts can be utilized in a large variety of imaging processes, notnecessarily connected to ophthalmic applications. In general, the method300 can be applied for imaging for invasive and non-invasive medicalprocedures. It can also be applied in a variety of manners for imagingfor material processing, or for a non-invasive analysis of materialfatigue, used from the airline industry to the nuclear industry, to namea few.

In any of these applications the imaging method 300 can include thefollowing steps.

In step 310, positioning an object relative to an imaging system,wherein a shape of the object is describable in terms of one or moreshape parameter and the orientation of the object is describable interms of one or more orientation parameter.

In step 320, creating scan data by determining a coordinate of theobject at a set of points along an arc.

In step 330, determining the object shape and orientation parameters andobject position parameters based on the scan data 330.

The object can be a portion of a spherical surface layer, as e.g. shownin FIG. 4B, the determined object shape parameter SP1 can be a radius ofthe spherical surface layer R, and the object position parameters can bethe XY coordinates of the center of the sphere, as e.g. expressed inEqs. (1)-(5).

Or, the object can be an ellipsoid, the shape parameters SPj can be thelengths of the three axes of the ellipsoid, the orientation parametersOPj can be the angles of the unit vectors representing the direction ofthe main axes, and the position parameters PPj can be the coordinates ofthe center of the ellipsoid.

While the method 300 was described with reference to the figures of theophthalmic application, a very wide variety of imaging applications isenvisioned here. An object which can reflect or alter light propagationin any way can be imaged by the imaging method 300. An object which canbe characterized in terms of shape parameters can be imagined by themethod 300. In some applications developed for studying materialquality, the corrugation of material surfaces can be imaged. In some ofthese applications the shape parameter can be a typical feature size onthe corrugated surface, or a typical unevenness of the grain or domainsize of the material. In engineering applications where wear and fatigueof machine parts can be investigated, the shape of the machine part maybe known from the design process, and the imaging method 300 may imagethe degree of deterioration or change of these known shape parameters,such as a narrowing of a diameter of a wire or a cross section of abeam.

Further, the imaging method 300 so far has been described in terms ofclosed objects, i.e. objects surrounded by a closed surface. In otherembodiments, “open objects” can be imaged as well, which are surroundedby open surfaces. A class of open surfaces includes surfaces withboundaries or edges. Examples of open objects include portions of closedobjects, e.g. a portion of a sphere or an ellipsoid, having a circularor an elliptic boundary or edge. Other examples include varioussurfaces, imaged for any engineering, quality control, materialdiagnostics and characterization purpose. A particular class ofapplication of the imaging method 300 is for open objects which are nottransparent. Many examples of such non-transparent open objects areimaged for a variety of reasons by the imaging method 300.

In many of these applications, the creating the scan data step 320 mayprovide sufficient data to determine the shape parameters, orientationparameters and position parameters of the imaged object, using theknowledge that the object can be characterized in terms of theparticular shape parameters. In some other applications which imageobjects without an a priori knowledge of the object's shape, a processormay propose various shapes and analyze the scan data in terms of theproposed shapes. Using some fitting criteria, the processor may decidewhich proposed shape is the most appropriate for the imaged object andproceed with the determination of the object shape parameter and objectposition parameter.

In some embodiments the object can be an anterior lens surface layer ofan eye, the object shape parameter a radius of the anterior lens surfacelayer, and the object position parameters the coordinates of a center ofthe anterior lens surface.

As above, the determining the object position parameters in step 330 caninclude imaging the object with at least one of an optical coherencetomography (OCT) method, an ultrasound-based method, a microscopicmethod and an interference based method.

The determining the object shape parameter and object positionparameters step 330 can include creating auxiliary scan data bydetermining a coordinate of the object at an auxiliary set of pointsalong an auxiliary arc. In some embodiments, this step can be practicedif the scan data along the original arc of step 320 is insufficient todetermine the object's shape and position parameters. The arc of step320 and the auxiliary arc of step 330 can be analogous to the arcs 241and 242 of FIGS. 4A-C.

In some embodiments the object's coordinate is a Z coordinate of anobject layer, and the arc is a portion of an intersection line where ascanning cylinder intersects the object layer.

The determining the object shape parameter in step 330 can includedetermining the Z coordinate of the object layer at the auxiliary set ofpoints along an intersection line where an auxiliary cylinder intersectsthe object layer. In analogy to FIG. 4C, the scanning cylinder and theauxiliary cylinder can be essentially concentric, sharing a Z axis.

The determining the object shape parameter and object position parameterstep 330 can include extracting an amplitude and a phase of the scandata, and determining a center of the object layer based on theextracted amplitude and phase.

In various implementations, the object position parameter can be aparameter of a center of the object layer or a perimeter of the objectlayer.

As above, because of the high efficiency of the method 300, in someimplementations carrying out a single scan data creating step 320 can besufficient, thus no additional scans are needed after the first scan,and possibly the first auxiliary scan. This is in contrast to existingsystems, where the shape or position parameter may be determinediteratively, by repeating the scanning step 320.

Also, as above, the object position parameter and the object shapeparameter can be carried out in an integrated manner.

FIG. 6B illustrates an aspect of the above imaging methods 100 and 300.Since these methods are very efficient, they can deliver the targetposition data in a timely manner. This enables implementations toperform the imaging methods 100 or 300 repeatedly e.g. during a surgicalprocedure, to provide essentially real time or slightly delayed timeposition information. Then, if for whatever reason there was a change inthe target region, such as the patient having moved his or her eye, theimaging system may be capable of determining updates to the targetposition parameter in a near real time manner, so that the surgicalpattern can be shifted accordingly and the surgical laser can be appliedaccording to the shifted surgical pattern. This (near) real timecapability enhances the precision of the ophthalmic surgical procedureeven more.

Such a (near) real time imaging and guiding method 400 for eye surgerycan include the steps of:

(a) positioning an eye relative to a surgical laser system, the surgicallaser system having a surgical position parameter and the eye having alens—step 410;

(b) determining position data of a lens target region along a scanningarc—step 420;

(c) determining a lens position parameter based on the positiondata—step 430;

(d) adjusting the surgical position parameter according to thedetermined lens position parameter—step 440; and

(e) repeating steps (b)-(d) during the eye surgery to readjust thesurgical position parameter—step 450.

The method 400 can be used e.g. for surgeries where the lens target isone of an anterior lens surface, an anterior surface defined by a pupil,a lens target region and a posterior lens surface.

In analogy to FIGS. 4A-E, the determining the lens position parametersstep 430 can include extracting an amplitude and a phase of the positiondata, and then determining a position parameter of a center of the lenstarget based on the amplitude and phase of the position data.

In some implementations, the adjusting a surgical position parameterstep 440 can include adjusting a parameter of a surgical pattern centerto align a surgical pattern in three dimensions with respect to acharacteristic feature of the lens.

FIGS. 7-17 illustrate embodiments of a laser surgery system.

One important aspect of laser surgical procedures is precise control andaiming of a laser beam, e.g., the beam position and beam focusing. Lasersurgery systems can be designed to include laser control and aimingtools to precisely target laser pulses to a particular target inside thetissue. In various nanosecond photodisruptive laser surgical systems,such as the Nd:YAG laser systems, the required level of targetingprecision is relatively low. This is in part because the laser energyused is relatively high and thus the affected tissue area is alsorelatively large, often covering an impacted area with a dimension inthe hundreds of microns. The time between laser pulses in such systemstend to be long and manual controlled targeting is feasible and iscommonly used. One example of such manual targeting mechanisms is abiomicroscope to visualize the target tissue in combination with asecondary laser source used as an aiming beam. The surgeon manuallymoves the focus of a laser focusing lens, usually with a joystickcontrol, which is parfocal (with or without an offset) with their imagethrough the microscope, so that the surgical beam or aiming beam is inbest focus on the intended target.

Such techniques designed for use with low repetition rate laser surgicalsystems may be difficult to use with high repetition rate lasersoperating at thousands of shots per second and relatively low energy perpulse. In surgical operations with high repetition rate lasers, muchhigher precision may be required due to the small effects of each singlelaser pulse and much higher positioning speed may be required due to theneed to deliver thousands of pulses to new treatment areas very quickly.

Examples of high repetition rate pulsed lasers for laser surgicalsystems include pulsed lasers at a pulse repetition rate of thousands ofshots per second or higher with relatively low energy per pulse. Suchlasers use relatively low energy per pulse to localize the tissue effectcaused by laser-induced photodisruption, e.g., the impacted tissue areaby photodisruption on the order of microns or tens of microns. Thislocalized tissue effect can improve the precision of the laser surgeryand can be desirable in certain surgical procedures such as laser eyesurgery. In one example of such surgery, placement of many hundred,thousands or millions of contiguous, nearly contiguous or pulsesseparated by known distances, can be used to achieve certain desiredsurgical effects, such as tissue incisions, separations orfragmentation.

Various surgical procedures using high repetition rate photodisruptivelaser surgical systems with shorter laser pulse durations may requirehigh precision in positioning each pulse in the target tissue undersurgery both in an absolute position with respect to a target locationon the target tissue and a relative position with respect to precedingpulses. For example, in some cases, laser pulses may be required to bedelivered next to each other with an accuracy of a few microns withinthe time between pulses, which can be on the order of microseconds.Because the time between two sequential pulses is short and theprecision requirement for the pulse alignment is high, manual targetingas used in low repetition rate pulsed laser systems may be no longeradequate or feasible.

One technique to facilitate and control precise, high speed positioningrequirement for delivery of laser pulses into the tissue is attaching aapplanation plate made of a transparent material such as a glass with apredefined contact surface to the tissue so that the contact surface ofthe applanation plate forms a well-defined optical interface with thetissue. This well-defined interface can facilitate transmission andfocusing of laser light into the tissue to control or reduce opticalaberrations or variations (such as due to specific eye opticalproperties or changes that occur with surface drying) that are mostcritical at the air-tissue interface, which in the eye is at theanterior surface of the cornea. Contact lenses can be designed forvarious applications and targets inside the eye and other tissues,including ones that are disposable or reusable. The contact glass orapplanation plate on the surface of the target tissue can be used as areference plate relative to which laser pulses are focused through theadjustment of focusing elements within the laser delivery system. Thisuse of a contact glass or applanation plate provides better control ofthe optical qualities of the tissue surface and thus allow laser pulsesto be accurately placed at a high speed at a desired location(interaction point) in the target tissue relative to the applanationreference plate with little optical distortion of the laser pulses.

One way for implementing an applanation plate on an eye is to use theapplanation plate to provide a positional reference for delivering thelaser pulses into a target tissue in the eye. This use of theapplanation plate as a positional reference can be based on the knowndesired location of laser pulse focus in the target with sufficientaccuracy prior to firing the laser pulses and that the relativepositions of the reference plate and the individual internal tissuetarget must remain constant during laser firing. In addition, thismethod can require the focusing of the laser pulse to the desiredlocation to be predictable and repeatable between eyes or in differentregions within the same eye. In practical systems, it can be difficultto use the applanation plate as a positional reference to preciselylocalize laser pulses intraocularly because the above conditions may notbe met in practical systems.

For example, if the crystalline lens is the surgical target, the precisedistance from the reference plate on the surface of the eye to thetarget tends to vary due to the presence of collapsible structures, suchas the cornea itself, the anterior chamber, and the iris. Not only istheir considerable variability in the distance between the applanatedcornea and the lens between individual eyes, but there can also bevariation within the same eye depending on the specific surgical andapplanation technique used by the surgeon. In addition, there can bemovement of the targeted lens tissue relative to the applanated surfaceduring the firing of the thousands of laser pulses required forachieving the surgical effect, further complicating the accuratedelivery of pulses. In addition, structure within the eye may move dueto the build-up of photodisruptive byproducts, such as cavitationbubbles. For example, laser pulses delivered to the crystalline lens cancause the lens capsule to bulge forward, requiring adjustment to targetthis tissue for subsequent placement of laser pulses. Furthermore, itcan be difficult to use computer models and simulations to predict, withsufficient accuracy, the actual location of target tissues after theapplanation plate is removed and to adjust placement of laser pulses toachieve the desired localization without applanation in part because ofthe highly variable nature of applanation effects, which can depend onfactors particular to the individual cornea or eye, and the specificsurgical and applanation technique used by a surgeon.

In addition to the physical effects of applanation thatdisproportionably affect the localization of internal tissue structures,in some surgical processes, it may be desirable for a targeting systemto anticipate or account for nonlinear characteristics ofphotodisruption which can occur when using short pulse duration lasers.Photodisruption is a nonlinear optical process in the tissue materialand can cause complications in beam alignment and beam targeting. Forexample, one of the nonlinear optical effects in the tissue materialwhen interacting with laser pulses during the photodisruption is thatthe refractive index of the tissue material experienced by the laserpulses is no longer a constant but varies with the intensity of thelight. Because the intensity of the light in the laser pulses variesspatially within the pulsed laser beam, along and across the propagationdirection of the pulsed laser beam, the refractive index of the tissuematerial also varies spatially. One consequence of this nonlinearrefractive index is self-focusing or self-defocusing in the tissuematerial that changes the actual focus of and shifts the position of thefocus of the pulsed laser beam inside the tissue. Therefore, a precisealignment of the pulsed laser beam to each target tissue position in thetarget tissue may also need to account for the nonlinear optical effectsof the tissue material on the laser beam. In addition, it may benecessary to adjust the energy in each pulse to deliver the samephysical effect in different regions of the target due to differentphysical characteristics, such as hardness, or due to opticalconsiderations such as absorption or scattering of laser pulse lighttraveling to a particular region. In such cases, the differences innon-linear focusing effects between pulses of different energy valuescan also affect the laser alignment and laser targeting of the surgicalpulses.

Thus, in surgical procedures in which non superficial structures aretargeted, the use of a superficial applanation plate based on apositional reference provided by the applanation plate may beinsufficient to achieve precise laser pulse localization in internaltissue targets. The use of the applanation plate as the reference forguiding laser delivery may require measurements of the thickness andplate position of the applanation plate with high accuracy because thedeviation from nominal is directly translated into a depth precisionerror. High precision applanation lenses can be costly, especially forsingle use disposable applanation plates.

The techniques, apparatus and systems described in this document can beimplemented in ways that provide a targeting mechanism to deliver shortlaser pulses through an applanation plate to a desired localizationinside the eye with precision and at a high speed without requiring theknown desired location of laser pulse focus in the target withsufficient accuracy prior to firing the laser pulses and withoutrequiring that the relative positions of the reference plate and theindividual internal tissue target remain constant during laser firing.As such, the present techniques, apparatus and systems can be used forvarious surgical procedures where physical conditions of the targettissue under surgery tend to vary and are difficult to control and thedimension of the applanation lens tends to vary from one lens toanother. The present techniques, apparatus and systems may also be usedfor other surgical targets where distortion or movement of the surgicaltarget relative to the surface of the structure is present or non-linearoptical effects make precise targeting problematic. Examples for suchsurgical targets different from the eye include the heart, deeper tissuein the skin and others.

The present techniques, apparatus and systems can be implemented in waysthat maintain the benefits provided by an applanation plate, including,for example, control of the surface shape and hydration, as well asreductions in optical distortion, while providing for the preciselocalization of photodisruption to internal structures of the applanatedsurface. This can be accomplished through the use of an integratedimaging device to localize the target tissue relative to the focusingoptics of the delivery system. The exact type of imaging device andmethod can vary and may depend on the specific nature of the target andthe required level of precision.

An applanation lens may be implemented with another mechanism to fix theeye to prevent translational and rotational movement of the eye.Examples of such fixation devices include the use of a suction ring.Such fixation mechanism can also lead to unwanted distortion or movementof the surgical target. The present techniques, apparatus and systemscan be implemented to provide, for high repetition rate laser surgicalsystems that utilize an applanation plate and/or fixation means fornon-superficial surgical targets, a targeting mechanism to provideintraoperative imaging to monitor such distortion and movement of thesurgical target.

Specific examples of laser surgical techniques, apparatus and systemsare described below to use an optical imaging module to capture imagesof a target tissue to obtain positioning information of the targettissue, e.g., before and during a surgical procedure. Such obtainedpositioning information can be used to control the positioning andfocusing of the surgical laser beam in the target tissue to provideaccurate control of the placement of the surgical laser pulses in highrepetition rate laser systems. In one implementation, during a surgicalprocedure, the images obtained by the optical imaging module can be usedto dynamically control the position and focus of the surgical laserbeam. In addition, lower energy and shot laser pulses tend to besensitive to optical distortions, such a laser surgical system canimplement an applanation plate with a flat or curved interface attachingto the target tissue to provide a controlled and stable opticalinterface between the target tissue and the surgical laser system and tomitigate and control optical aberrations at the tissue surface.

As an example, FIG. 7 shows a laser surgical system based on opticalimaging and applanation. This system includes a pulsed laser 1010 toproduce a surgical laser beam 1012 of laser pulses, and an optics module1020 to receive the surgical laser beam 1012 and to focus and direct thefocused surgical laser beam 1022 onto a target tissue 1001, such as aneye, to cause photodisruption in the target tissue 1001. An applanationplate can be provided to be in contact with the target tissue 1001 toproduce an interface for transmitting laser pulses to the target tissue1001 and light coming from the target tissue 1001 through the interface.Notably, an optical imaging device 1030 is provided to capture light1050 carrying target tissue images 1050 or imaging information from thetarget tissue 1001 to create an image of the target tissue 1001. Theimaging signal 1032 from the imaging device 1030 is sent to a systemcontrol module 1040. The system control module 1040 operates to processthe captured images from the image device 1030 and to control the opticsmodule 1020 to adjust the position and focus of the surgical laser beam1022 at the target tissue 1001 based on information from the capturedimages. The optics module 1020 can include one or more lenses and mayfurther include one or more reflectors. A control actuator can beincluded in the optics module 1020 to adjust the focusing and the beamdirection in response to a beam control signal 1044 from the systemcontrol module 1040. The control module 1040 can also control the pulsedlaser 1010 via a laser control signal 1042.

The optical imaging device 1030 may be implemented to produce an opticalimaging beam that is separate from the surgical laser beam 1022 to probethe target tissue 1001 and the returned light of the optical imagingbeam is captured by the optical imaging device 1030 to obtain the imagesof the target tissue 1001. One example of such an optical imaging device1030 is an optical coherence tomography (OCT) imaging module which usestwo imaging beams, one probe beam directed to the target tissue 1001thought the applanation plate and another reference beam in a referenceoptical path, to optically interfere with each other to obtain images ofthe target tissue 1001. In other implementations, the optical imagingdevice 1030 can use scattered or reflected light from the target tissue1001 to capture images without sending a designated optical imaging beamto the target tissue 1001. For example, the imaging device 1030 can be asensing array of sensing elements such as CCD or CMS sensors. Forexample, the images of photodisruption byproduct produced by thesurgical laser beam 1022 may be captured by the optical imaging device1030 for controlling the focusing and positioning of the surgical laserbeam 1022. When the optical imaging device 1030 is designed to guidesurgical laser beam alignment using the image of the photodisruptionbyproduct, the optical imaging device 1030 captures images of thephotodisruption byproduct such as the laser-induced bubbles or cavities.The imaging device 1030 may also be an ultrasound imaging device tocapture images based on acoustic images.

The system control module 1040 processes image data from the imagingdevice 1030 that includes the position offset information for thephotodisruption byproduct from the target tissue position in the targettissue 1001. Based on the information obtained from the image, the beamcontrol signal 1044 is generated to control the optics module 1020 whichadjusts the laser beam 1022. A digital processing unit can be includedin the system control module 1040 to perform various data processing forthe laser alignment.

The above techniques and systems can be used deliver high repetitionrate laser pulses to subsurface targets with a precision required forcontiguous pulse placement, as needed for cutting or volume disruptionapplications. This can be accomplished with or without the use of areference source on the surface of the target and can take into accountmovement of the target following applanation or during placement oflaser pulses.

The applanation plate in the present systems is provided to facilitateand control precise, high speed positioning requirement for delivery oflaser pulses into the tissue. Such an applanation plate can be made of atransparent material such as a glass with a predefined contact surfaceto the tissue so that the contact surface of the applanation plate formsa well-defined optical interface with the tissue. This well-definedinterface can facilitate transmission and focusing of laser light intothe tissue to control or reduce optical aberrations or variations (suchas due to specific eye optical properties or changes that occur withsurface drying) that are most critical at the air-tissue interface,which in the eye is at the anterior surface of the cornea. A number ofcontact lenses have been designed for various applications and targetsinside the eye and other tissues, including ones that are disposable orreusable. The contact glass or applanation plate on the surface of thetarget tissue is used as a reference plate relative to which laserpulses are focused through the adjustment of focusing elements withinthe laser delivery system relative. Inherent in such an approach are theadditional benefits afforded by the contact glass or applanation platedescribed previously, including control of the optical qualities of thetissue surface. Accordingly, laser pulses can be accurately placed at ahigh speed at a desired location (interaction point) in the targettissue relative to the applanation reference plate with little opticaldistortion of the laser pulses.

The optical imaging device 1030 in FIG. 7 captures images of the targettissue 1001 via the applanation plate. The control module 1040 processesthe captured images to extract position information from the capturedimages and uses the extracted position information as a positionreference or guide to control the position and focus of the surgicallaser beam 1022. This imaging-guided laser surgery can be implementedwithout relying on the applanation plate as a position reference becausethe position of the applanation plate tends to change due to variousfactors as discussed above. Hence, although the applanation plateprovides a desired optical interface for the surgical laser beam toenter the target tissue and to capture images of the target tissue, itmay be difficult to use the applanation plate as a position reference toalign and control the position and focus of the surgical laser beam foraccurate delivery of laser pulses. The imaging-guided control of theposition and focus of the surgical laser beam based on the imagingdevice 1030 and the control module 1040 allows the images of the targettissue 1001, e.g., images of inner structures of an eye, to be used asposition references, without using the applanation plate to provide aposition reference.

In addition to the physical effects of applanation thatdisproportionably affect the localization of internal tissue structures,in some surgical processes, it may be desirable for a targeting systemto anticipate or account for nonlinear characteristics ofphotodisruption which can occur when using short pulse duration lasers.Photodisruption can cause complications in beam alignment and beamtargeting. For example, one of the nonlinear optical effects in thetissue material when interacting with laser pulses during thephotodisruption is that the refractive index of the tissue materialexperienced by the laser pulses is no longer a constant but varies withthe intensity of the light. Because the intensity of the light in thelaser pulses varies spatially within the pulsed laser beam, along andacross the propagation direction of the pulsed laser beam, therefractive index of the tissue material also varies spatially. Oneconsequence of this nonlinear refractive index is self-focusing orself-defocusing in the tissue material that changes the actual focus ofand shifts the position of the focus of the pulsed laser beam inside thetissue. Therefore, a precise alignment of the pulsed laser beam to eachtarget tissue position in the target tissue may also need to account forthe nonlinear optical effects of the tissue material on the laser beam.The energy of the laser pulses may be adjusted to deliver the samephysical effect in different regions of the target due to differentphysical characteristics, such as hardness, or due to opticalconsiderations such as absorption or scattering of laser pulse lighttraveling to a particular region. In such cases, the differences innon-linear focusing effects between pulses of different energy valuescan also affect the laser alignment and laser targeting of the surgicalpulses. In this regard, the direct images obtained from the target issueby the imaging device 1030 can be used to monitor the actual position ofthe surgical laser beam 1022 which reflects the combined effects ofnonlinear optical effects in the target tissue and provide positionreferences for control of the beam position and beam focus.

The techniques, apparatus and systems described here can be used incombination of an applanation plate to provide control of the surfaceshape and hydration, to reduce optical distortion, and provide forprecise localization of photodisruption to internal structures throughthe applanated surface. The imaging-guided control of the beam positionand focus described here can be applied to surgical systems andprocedures that use means other than applanation plates to fix the eye,including the use of a suction ring which can lead to distortion ormovement of the surgical target.

The following sections first describe examples of techniques, apparatusand systems for automated imaging-guided laser surgery based on varyingdegrees of integration of imaging functions into the laser control partof the systems. An optical or other modality imaging module, such as anOCT imaging module, can be used to direct a probe light or other type ofbeam to capture images of a target tissue, e.g., structures inside aneye. A surgical laser beam of laser pulses such as femtosecond orpicosecond laser pulses can be guided by position information in thecaptured images to control the focusing and positioning of the surgicallaser beam during the surgery. Both the surgical laser beam and theprobe light beam can be sequentially or simultaneously directed to thetarget tissue during the surgery so that the surgical laser beam can becontrolled based on the captured images to ensure precision and accuracyof the surgery.

Such imaging-guided laser surgery can be used to provide accurate andprecise focusing and positioning of the surgical laser beam during thesurgery because the beam control is based on images of the target tissuefollowing applanation or fixation of the target tissue, either justbefore or nearly simultaneously with delivery of the surgical pulses.Notably, certain parameters of the target tissue such as the eyemeasured before the surgery may change during the surgery due to variousfactor such as preparation of the target tissue (e.g., fixating the eyeto an applanation lens) and the alternation of the target tissue by thesurgical operations. Therefore, measured parameters of the target tissueprior to such factors and/or the surgery may no longer reflect thephysical conditions of the target tissue during the surgery. The presentimaging-guided laser surgery can mitigate technical issues in connectionwith such changes for focusing and positioning the surgical laser beambefore and during the surgery.

The present imaging-guided laser surgery may be effectively used foraccurate surgical operations inside a target tissue. For example, whenperforming laser surgery inside the eye, laser light is focused insidethe eye to achieve optical breakdown of the targeted tissue and suchoptical interactions can change the internal structure of the eye. Forexample, the crystalline lens can change its position, shape, thicknessand diameter during accommodation, not only between prior measurementand surgery but also during surgery. Attaching the eye to the surgicalinstrument by mechanical means can change the shape of the eye in a notwell defined way and further, the change can vary during surgery due tovarious factors, e.g., patient movement. Attaching means includefixating the eye with a suction ring and applanating the eye with a flator curved lens. These changes amount to as much as a few millimeters.Mechanically referencing and fixating the surface of the eye such as theanterior surface of the cornea or limbus does not work well whenperforming precision laser microsurgery inside the eye.

The post preparation or near simultaneous imaging in the presentimaging-guided laser surgery can be used to establish three-dimensionalpositional references between the inside features of the eye and thesurgical instrument in an environment where changes occur prior to andduring surgery. The positional reference information provided by theimaging prior to applanation and/or fixation of the eye, or during theactual surgery reflects the effects of changes in the eye and thusprovides an accurate guidance to focusing and positioning of thesurgical laser beam. A system based on the present imaging-guided lasersurgery can be configured to be simple in structure and cost efficient.For example, a portion of the optical components associated with guidingthe surgical laser beam can be shared with optical components forguiding the probe light beam for imaging the target tissue to simplifythe device structure and the optical alignment and calibration of theimaging and surgical light beams.

The imaging-guided laser surgical systems described below use the OCTimaging as an example of an imaging instrument and other non-OCT imagingdevices may also be used to capture images for controlling the surgicallasers during the surgery. As illustrated in the examples below,integration of the imaging and surgical subsystems can be implemented tovarious degrees. In the simplest form without integrating hardware, theimaging and laser surgical subsystems are separated and can communicateto one another through interfaces. Such designs can provide flexibilityin the designs of the two subsystems. Integration between the twosubsystems, by some hardware components such as a patient interface,further expands the functionality by offering better registration ofsurgical area to the hardware components, more accurate calibration andmay improve workflow. As the degree of integration between the twosubsystems increases, such a system may be made increasinglycost-efficient and compact and system calibration will be furthersimplified and more stable over time. Examples for imaging-guided lasersystems in FIGS. 8-16 are integrated at various degrees of integration.

One implementation of a present imaging-guided laser surgical system,for example, includes a surgical laser that produces a surgical laserbeam of surgical laser pulses that cause surgical changes in a targettissue under surgery; a patient interface mount that engages a patientinterface in contact with the target tissue to hold the target tissue inposition; and a laser beam delivery module located between the surgicallaser and the patient interface and configured to direct the surgicallaser beam to the target tissue through the patient interface. Thislaser beam delivery module is operable to scan the surgical laser beamin the target tissue along a predetermined surgical pattern. This systemalso includes a laser control module that controls operation of thesurgical laser and controls the laser beam delivery module to producethe predetermined surgical pattern and an OCT module positioned relativeto the patient interface to have a known spatial relation with respectto the patient interface and the target issue fixed to the patientinterface. The OCT module is configured to direct an optical probe beamto the target tissue and receive returned probe light of the opticalprobe beam from the target tissue to capture OCT images of the targettissue while the surgical laser beam is being directed to the targettissue to perform an surgical operation so that the optical probe beamand the surgical laser beam are simultaneously present in the targettissue. The OCT module is in communication with the laser control moduleto send information of the captured OCT images to the laser controlmodule.

In addition, the laser control module in this particular system respondsto the information of the captured OCT images to operate the laser beamdelivery module in focusing and scanning of the surgical laser beam andadjusts the focusing and scanning of the surgical laser beam in thetarget tissue based on positioning information in the captured OCTimages.

In some implementations, acquiring a complete image of a target tissuemay not be necessary for registering the target to the surgicalinstrument and it may be sufficient to acquire a portion of the targettissue, e.g., a few points from the surgical region such as natural orartificial landmarks. For example, a rigid body has six degrees offreedom in 3D space and six independent points would be sufficient todefine the rigid body. When the exact size of the surgical region is notknown, additional points are needed to provide the positional reference.In this regard, several points can be used to determine the position andthe curvature of the anterior and posterior surfaces, which are normallydifferent, and the thickness and diameter of the crystalline lens of thehuman eye. Based on these data a body made up from two halves ofellipsoid bodies with given parameters can approximate and visualize acrystalline lens for practical purposes. In another implementation,information from the captured image may be combined with informationfrom other sources, such as pre-operative measurements of lens thicknessthat are used as an input for the controller.

FIG. 8 shows one example of an imaging-guided laser surgical system withseparated laser surgical system 2100 and imaging system 2200. The lasersurgical system 2100 includes a laser engine 2130 with a surgical laserthat produces a surgical laser beam 2160 of surgical laser pulses. Alaser beam delivery module 2140 is provided to direct the surgical laserbeam 2160 from the laser engine 2130 to the target tissue 1001 through apatient interface 2150 and is operable to scan the surgical laser beam2160 in the target tissue 1001 along a predetermined surgical pattern. Alaser control module 2120 is provided to control the operation of thesurgical laser in the laser engine 2130 via a communication channel 2121and controls the laser beam delivery module 2140 via a communicationchannel 2122 to produce the predetermined surgical pattern. A patientinterface mount is provided to engage the patient interface 2150 incontact with the target tissue 1001 to hold the target tissue 1001 inposition. The patient interface 2150 can be implemented to include acontact lens or applanation lens with a flat or curved surface toconformingly engage to the anterior surface of the eye and to hold theeye in position.

The imaging system 2200 in FIG. 8 can be an OCT module positionedrelative to the patient interface 2150 of the surgical system 2100 tohave a known spatial relation with respect to the patient interface 2150and the target issue 1001 fixed to the patient interface 2150. This OCTmodule 2200 can be configured to have its own patient interface 2240 forinteracting with the target tissue 1001. The imaging system 2200includes an imaging control module 2220 and an imaging sub-system 2230.The sub-system 2230 includes a light source for generating imaging beam2250 for imaging the target 1001 and an imaging beam delivery module todirect the optical probe beam or imaging beam 2250 to the target tissue1001 and receive returned probe light 2260 of the optical imaging beam2250 from the target tissue 1001 to capture OCT images of the targettissue 1001. Both the optical imaging beam 2250 and the surgical beam2160 can be simultaneously directed to the target tissue 1001 to allowfor sequential or simultaneous imaging and surgical operation.

As illustrated in FIG. 8, communication interfaces 2110 and 2210 areprovided in both the laser surgical system 2100 and the imaging system2200 to facilitate the communications between the laser control by thelaser control module 2120 and imaging by the imaging system 2200 so thatthe OCT module 2200 can send information of the captured OCT images tothe laser control module 2120. The laser control module 2120 in thissystem responds to the information of the captured OCT images to operatethe laser beam delivery module 2140 in focusing and scanning of thesurgical laser beam 2160 and dynamically adjusts the focusing andscanning of the surgical laser beam 2160 in the target tissue 1001 basedon positioning information in the captured OCT images. The integrationbetween the laser surgical system 2100 and the imaging system 2200 ismainly through communication between the communication interfaces 2110and 2210 at the software level.

In this and other examples, various subsystems or devices may also beintegrated. For example, certain diagnostic instruments such aswavefront aberrometers, corneal topography measuring devices may beprovided in the system, or pre-operative information from these devicescan be utilized to augment intra-operative imaging.

FIG. 9 shows an example of an imaging-guided laser surgical system withadditional integration features. The imaging and surgical systems sharea common patient interface 3300 which immobilizes target tissue 1001(e.g., the eye) without having two separate patient interfaces as inFIG. 8. The surgical beam 3210 and the imaging beam 3220 are combined atthe patient interface 3330 and are directed to the target 1001 by thecommon patient interface 3300. In addition, a common control module 3100is provided to control both the imaging sub-system 2230 and the surgicalpart (the laser engine 2130 and the beam delivery system 2140). Thisincreased integration between imaging and surgical parts allows accuratecalibration of the two subsystems and the stability of the position ofthe patient and surgical volume. A common housing 3400 is provided toenclose both the surgical and imaging subsystems. When the two systemsare not integrated into a common housing, the common patient interface3300 can be part of either the imaging or the surgical subsystem.

FIG. 10 shows an example of an imaging-guided laser surgical systemwhere the laser surgical system and the imaging system share both acommon beam delivery module 4100 and a common patient interface 4200.This integration further simplifies the system structure and systemcontrol operation.

In one implementation, the imaging system in the above and otherexamples can be an optical computed tomography (OCT) system and thelaser surgical system is a femtosecond or picosecond laser basedophthalmic surgical system. In OCT, light from a low coherence,broadband light source such as a super luminescent diode is split intoseparate reference and signal beams. The signal beam is the imaging beamsent to the surgical target and the returned light of the imaging beamis collected and recombined coherently with the reference beam to forman interferometer. Scanning the signal beam perpendicularly to theoptical axis of the optical train or the propagation direction of thelight provides spatial resolution in the x-y direction while depthresolution comes from extracting differences between the path lengths ofthe reference arm and the returned signal beam in the signal arm of theinterferometer. While the x-y scanner of different OCT implementationsare essentially the same, comparing the path lengths and getting z-scaninformation can happen in different ways. In one implementation known asthe time domain OCT, for example, the reference arm is continuouslyvaried to change its path length while a photodetector detectsinterference modulation in the intensity of the recombined beam. In adifferent implementation, the reference arm is essentially static andthe spectrum of the combined light is analyzed for interference. TheFourier transform of the spectrum of the combined beam provides spatialinformation on the scattering from the interior of the sample. Thismethod is known as the spectral domain or Fourier OCT method. In adifferent implementation known as a frequency swept OCT (S. R. Chinn,et. al., Opt. Lett. 22, 1997), a narrowband light source is used withits frequency swept rapidly across a spectral range. Interferencebetween the reference and signal arms is detected by a fast detector anddynamic signal analyzer. An external cavity tuned diode laser orfrequency tuned of frequency domain mode-locked (FDML) laser developedfor this purpose (R. Huber et. Al. Opt. Express, 13, 2005) (S. H. Yun,IEEE J. of Sel. Q. El. 3(4) p. 1087-1096, 1997) can be used in theseexamples as a light source. A femtosecond laser used as a light sourcein an OCT system can have sufficient bandwidth and can provideadditional benefits of increased signal to noise ratios.

The OCT imaging device in the systems in this document can be used toperform various imaging functions. For example, the OCT can be used tosuppress complex conjugates resulting from the optical configuration ofthe system or the presence of the applanation plate, capture OCT imagesof selected locations inside the target tissue to providethree-dimensional positioning information for controlling focusing andscanning of the surgical laser beam inside the target tissue, or captureOCT images of selected locations on the surface of the target tissue oron the applanation plate to provide positioning registration forcontrolling changes in orientation that occur with positional changes ofthe target, such as from upright to supine. The OCT can be calibrated bya positioning registration process based on placement of marks ormarkers in one positional orientation of the target that can then bedetected by the OCT module when the target is in another positionalorientation. In other implementations, the OCT imaging system can beused to produce a probe light beam that is polarized to optically gatherthe information on the internal structure of the eye. The laser beam andthe probe light beam may be polarized in different polarizations. TheOCT can include a polarization control mechanism that controls the probelight used for said optical tomography to polarize in one polarizationwhen traveling toward the eye and in a different polarization whentraveling away from the eye. The polarization control mechanism caninclude, e.g., a wave-plate or a Faraday rotator.

The system in FIG. 10 is shown as a spectral OCT configuration and canbe configured to share the focusing optics part of the beam deliverymodule between the surgical and the imaging systems. The mainrequirements for the optics are related to the operating wavelength,image quality, resolution, distortion etc. The laser surgical system canbe a femtosecond laser system with a high numerical aperture systemdesigned to achieve diffraction limited focal spot sizes, e.g., about 2to 3 micrometers. Various femtosecond ophthalmic surgical lasers canoperate at various wavelengths such as wavelengths of around 1.05micrometer. The operating wavelength of the imaging device can beselected to be close to the laser wavelength so that the optics ischromatically compensated for both wavelengths. Such a system mayinclude a third optical channel, a visual observation channel such as asurgical microscope, to provide an additional imaging device to captureimages of the target tissue. If the optical path for this third opticalchannel shares optics with the surgical laser beam and the light of theOCT imaging device, the shared optics can be configured with chromaticcompensation in the visible spectral band for the third optical channeland the spectral bands for the surgical laser beam and the OCT imagingbeam.

FIG. 11 shows a particular example of the design in FIG. 9 where thescanner 5100 for scanning the surgical laser beam and the beamconditioner 5200 for conditioning (collimating and focusing) thesurgical laser beam are separate from the optics in the OCT imagingmodule 5300 for controlling the imaging beam for the OCT. The surgicaland imaging systems share an objective lens 5600 module and the patientinterface 3300. The objective lens 5600 directs and focuses both thesurgical laser beam and the imaging beam to the patient interface 3300and its focusing is controlled by the control module 3100. Two beamsplitters 5410 and 5420 are provided to direct the surgical and imagingbeams. The beam splitter 5420 is also used to direct the returnedimaging beam back into the OCT imaging module 5300. Two beam splitters5410 and 5420 also direct light from the target 1001 to a visualobservation optics unit 5500 to provide direct view or image of thetarget 1001. The unit 5500 can be a lens imaging system for the surgeonto view the target 1001 or a camera to capture the image or video of thetarget 1001. Various beam splitters can be used, such as dichroic andpolarization beam splitters, optical grating, holographic beam splitteror a combinations of these.

In some implementations, the optical components may be appropriatelycoated with antireflection coating for both the surgical and for the OCTwavelength to reduce glare from multiple surfaces of the optical beampath. Reflections would otherwise reduce the throughput of the systemand reduce the signal to noise ratio by increasing background light inthe OCT imaging unit. One way to reduce glare in the OCT is to rotatethe polarization of the return light from the sample by wave-plate ofFaraday isolator placed close to the target tissue and orient apolarizer in front of the OCT detector to preferentially detect lightreturned from the sample and suppress light scattered from the opticalcomponents.

In a laser surgical system, each of the surgical laser and the OCTsystem can have a beam scanner to cover the same surgical region in thetarget tissue. Hence, the beam scanning for the surgical laser beam andthe beam scanning for the imaging beam can be integrated to share commonscanning devices.

FIG. 12 shows an example of such a system in detail. In thisimplementation the x-y scanner 6410 and the z scanner 6420 are shared byboth subsystems. A common control 6100 is provided to control the systemoperations for both surgical and imaging operations. The OCT sub-systemincludes an OCT light source 6200 that produce the imaging light that issplit into an imaging beam and a reference beam by a beam splitter 6210.The imaging beam is combined with the surgical beam at the beam splitter6310 to propagate along a common optical path leading to the target1001. The scanners 6410 and 6420 and the beam conditioner unit 6430 arelocated downstream from the beam splitter 6310. A beam splitter 6440 isused to direct the imaging and surgical beams to the objective lens 5600and the patient interface 3300.

In the OCT sub-system, the reference beam transmits through the beamsplitter 6210 to an optical delay device 6220 and is reflected by areturn mirror 6230. The returned imaging beam from the target 1001 isdirected back to the beam splitter 6310 which reflects at least aportion of the returned imaging beam to the beam splitter 6210 where thereflected reference beam and the returned imaging beam overlap andinterfere with each other. A spectrometer detector 6240 is used todetect the interference and to produce OCT images of the target 1001.The OCT image information is sent to the control system 6100 forcontrolling the surgical laser engine 2130, the scanners 6410 and 6420and the objective lens 5600 to control the surgical laser beam. In oneimplementation, the optical delay device 6220 can be varied to changethe optical delay to detect various depths in the target tissue 1001.

If the OCT system is a time domain system, the two subsystems use twodifferent z-scanners because the two scanners operate in different ways.In this example, the z scanner of the surgical system operates bychanging the divergence of the surgical beam in the beam conditionerunit without changing the path lengths of the beam in the surgical beampath. On the other hand, the time domain OCT scans the z-direction byphysically changing the beam path by a variable delay or by moving theposition of the reference beam return mirror. After calibration, the twoz-scanners can be synchronized by the laser control module. Therelationship between the two movements can be simplified to a linear orpolynomial dependence, which the control module can handle oralternatively calibration points can define a look-up table to provideproper scaling. Spectral/Fourier domain and frequency swept source OCTdevices have no z-scanner, the length of the reference arm is static.Besides reducing costs, cross calibration of the two systems will berelatively straightforward. There is no need to compensate fordifferences arising from image distortions in the focusing optics orfrom the differences of the scanners of the two systems since they areshared.

In practical implementations of the surgical systems, the focusingobjective lens 5600 is slidably or movably mounted on a base and theweight of the objective lens is balanced to limit the force on thepatient's eye. The patient interface 3300 can include an applanationlens attached to a patient interface mount. The patient interface mountis attached to a mounting unit, which holds the focusing objective lens.This mounting unit is designed to ensure a stable connection between thepatient interface and the system in case of unavoidable movement of thepatient and allows gentler docking of the patient interface onto theeye. Various implementations for the focusing objective lens can be usedand one example is described in U.S. Pat. No. 5,336,215 to Hsueh. Thispresence of an adjustable focusing objective lens can change the opticalpath length of the optical probe light as part of the opticalinterferometer for the OCT sub-system. Movement of the objective lens5600 and patient interface 3300 can change the path length differencesbetween the reference beam and the imaging signal beam of the OCT in anuncontrolled way and this may degrade the OCT depth information detectedby the OCT. This would happen not only in time-domain but also inspectral/Fourier domain and frequency-swept OCT systems.

FIGS. 13-14 show exemplary imaging-guided laser surgical systems thataddress the technical issue associated with the adjustable focusingobjective lens.

The system in FIG. 13 provides a position sensing device 7110 coupled tothe movable focusing objective lens 7100 to measure the position of theobjective lens 7100 on a slideable mount and communicates the measuredposition to a control module 7200 in the OCT system. The control system6100 can control and move the position of the objective lens 7100 toadjust the optical path length traveled by the imaging signal beam forthe OCT operation and the position of the lens 7100 is measured andmonitored by the position encoder 7110 and direct fed to the OCT control7200. The control module 7200 in the OCT system applies an algorithm,when assembling a 3D image in processing the OCT data, to compensate fordifferences between the reference arm and the signal arm of theinterferometer inside the OCT caused by the movement of the focusingobjective lens 7100 relative to the patient interface 3300. The properamount of the change in the position of the lens 7100 computed by theOCT control module 7200 is sent to the control 6100 which controls thelens 7100 to change its position.

FIG. 14 shows another exemplary system where the return mirror 6230 inthe reference arm of the interferometer of the OCT system or at leastone part in an optical path length delay assembly of the OCT system isrigidly attached to the movable focusing objective lens 7100 so thesignal arm and the reference arm undergo the same amount of change inthe optical path length when the objective lens 7100 moves. As such, themovement of the objective lens 7100 on the slide is automaticallycompensated for path-length differences in the OCT system withoutadditional need for a computational compensation.

The above examples for imaging-guided laser surgical systems, the lasersurgical system and the OCT system use different light sources. In aneven more complete integration between the laser surgical system and theOCT system, a femtosecond surgical laser as a light source for thesurgical laser beam can also be used as the light source for the OCTsystem.

FIG. 15 shows an example where a femtosecond pulse laser in a lightmodule 9100 is used to generate both the surgical laser beam forsurgical operations and the probe light beam for OCT imaging. A beamsplitter 9300 is provided to split the laser beam into a first beam asboth the surgical laser beam and the signal beam for the OCT and asecond beam as the reference beam for the OCT. The first beam isdirected through an x-y scanner 6410 which scans the beam in the x and ydirections perpendicular to the propagation direction of the first beamand a second scanner (z scanner) 6420 that changes the divergence of thebeam to adjust the focusing of the first beam at the target tissue 1001.This first beam performs the surgical operations at the target tissue1001 and a portion of this first beam is back scattered to the patientinterface and is collected by the objective lens as the signal beam forthe signal arm of the optical interferometer of the OCT system. Thisreturned light is combined with the second beam that is reflected by areturn mirror 6230 in the reference arm and is delayed by an adjustableoptical delay element 6220 for a time-domain OCT to control the pathdifference between the signal and reference beams in imaging differentdepths of the target tissue 1001. The control system 9200 controls thesystem operations.

Surgical practice on the cornea has shown that a pulse duration ofseveral hundred femtoseconds may be sufficient to achieve good surgicalperformance, while for OCT of a sufficient depth resolution broaderspectral bandwidth generated by shorter pulses, e.g., below several tensof femtoseconds, are needed. In this context, the design of the OCTdevice dictates the duration of the pulses from the femtosecond surgicallaser.

FIG. 16 shows another imaging-guided system that uses a single pulsedlaser 9100 to produce the surgical light and the imaging light. Anonlinear spectral broadening media 9400 is placed in the output opticalpath of the femtosecond pulsed laser to use an optical non-linearprocess such as white light generation or spectral broadening to broadenthe spectral bandwidth of the pulses from a laser source of relativelylonger pulses, several hundred femtoseconds normally used in surgery.The media 9400 can be a fiber-optic material, for example. The lightintensity requirements of the two systems are different and a mechanismto adjust beam intensities can be implemented to meet such requirementsin the two systems. For example, beam steering minors, beam shutters orattenuators can be provided in the optical paths of the two systems toproperly control the presence and intensity of the beam when taking anOCT image or performing surgery in order to protect the patient andsensitive instruments from excessive light intensity.

In operation, the above examples in FIGS. 8-16 can be used to performimaging-guided laser surgery.

FIG. 17 shows one example of a method for performing laser surgery byusing an imaging-guided laser surgical system. This method uses apatient interface in the system to engage to and to hold a target tissueunder surgery in position and simultaneously directs a surgical laserbeam of laser pulses from a laser in the system and an optical probebeam from the OCT module in the system to the patient interface into thetarget tissue. The surgical laser beam is controlled to perform lasersurgery in the target tissue and the OCT module is operated to obtainOCT images inside the target tissue from light of the optical probe beamreturning from the target tissue. The position information in theobtained OCT images is applied in focusing and scanning of the surgicallaser beam to adjust the focusing and scanning of the surgical laserbeam in the target tissue before or during surgery.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

The invention claimed is:
 1. A method for guiding an eye surgery,comprising the steps of; creating first scan data by determining a depthof an eye target region at a first set of points along a first arc byone of an optical coherence tomographic (OCT) imaging system and aninterference-based imaging system: creating second scan data bydetermining a depth of the eye target region at a second set of pointsalong a second arc by the one of the OCT imaging system and theinterference-based imaging system; determining target region parametersbased on the first and second scan data by a computer controller;wherein the determining target region parameters step comprises: fittinga sinusoidal function or Fourier harmonics with at least one fittingparameter to the first and second scan data; and determining the targetregion parameters using the fitting parameter; and assisting anadjusting of one or more surgical position parameters according to thedetermined target region parameters by the computer controller.
 2. Themethod of claim 1, wherein: the eye target region is one of a cornealtarget region, an anterior lens surface, a posterior lens surface, alens target region, an ophthalmic layer, and a surface defined by apupil.
 3. The method of claim 1, wherein: at least one of the first arcand the second arc forms at least part of a closed loop.
 4. The methodof claim 1, wherein: the first arc is a portion of a first intersectionline where a first scanning surface intersects the eye target region;and the second arc is a portion of a second intersection line where asecond scanning surface intersects the eye target region.
 5. The methodof claim 1, wherein: the first arc is a portion of a first intersectionline where a first cylinder intersects the eye target region; and thesecond arc is a portion of a second intersection line where a secondcylinder intersects the eye target region.
 6. The method of claim 5,wherein: the first cylinder and the second cylinder are concentric,sharing a Z axis.
 7. The method of claim 5, wherein: a Z axis of thesecond cylinder is offset from a Z axis of the first cylinder.
 8. Themethod of claim 1, wherein the determining target region parameters stepcomprises: extracting scan characteristics from the first and secondscan data.
 9. The method of claim 8, wherein the extracting scancharacteristics step comprises: extracting a first amplitude and a firstphase of the first scan data; and extracting a second amplitude and asecond phase of the second scan data.
 10. The method of claim 9, whereinthe determining of target region parameters step comprises: determininga position parameter of a center of the target region based on the firstamplitude, first phase, second amplitude and second phase.
 11. Themethod of claim 9, wherein the determining of the target regionparameters step comprises: determining an object shape parameter of thetarget region based on the first amplitude, first phase, secondamplitude and second phase.
 12. The method of claim 9, wherein thedetermining of the target region parameters step comprises: determiningan object orientation parameter based on the first amplitude, firstphase, second amplitude and second phase.
 13. The method of claim 9,wherein the determining of the target region parameters step comprises:determining a position parameter update, related to a position of thetarget region and a reference point.
 14. The method of claim 1, whereinthe adjusting the surgical position parameter comprises: adjusting aposition parameter of a surgical pattern center to align the surgicalpattern center with a center of the target region.
 15. The method ofclaim 1, wherein the method contains: no more scans after the first scanand the second scan.
 16. The method of claim 1, wherein: the time fromthe starting of the first scanning step to the finishing of thedetermining the surgical position parameters step is no more than one of100 milliseconds, 1,000 milliseconds and 10,000 milliseconds.
 17. Themethod of claim 1, wherein: at least one of the first and second arc iselliptical.
 18. The method of claim 1, wherein: at least one of thefirst arc and the second arc is an open arc; and at least one of thefirst scan data and the second scan data have a maximum and a minimum.19. The method of claim 1, wherein the eye target region is a region ofa lens of the eye; the target region parameters comprise a shapeparameter of the lens, a tilt parameter of the lens, and a positionparameter of the lens.
 20. The method of claim 1, wherein: projectionsof the first arc and the second arc to a plane, transverse to an opticalaxis of the imaging system, are arcs.